Controls on the Global Distribution of Coastal Titanium-Zirconium Placers

Abstract

Exploration models for coastal titanium-zirconium placer deposits in general are poorly developed and reflect little understanding of the morphogenesis of this class of ore deposit. The increasing economic and strategic importance of these minerals requires a reevaluation of traditional approaches to deposit description. This paper, by describing the salient features of coastal T-Zr placers in five major placer-forming regions (Brazil, India/Sri Lanka, southeastern Africa, southeastern United States, and southwestern Australia), demonstrates that a morphogenetic approach can shed new light on placer development. Coastal placer coasts occur on Afro-type and Amero-type trailing continental margins, associated with a wide variety of types of continental shelves. They lie on wide or narrow coastal plains, but always are backed by a “great escarpment.” The hinterland usually consists of Precambrian metamorphic rocks, and often forms an elevated plateau. Intemediate sedimentary hosts and local tectonic movements are common contributing factors. Similarly, Quaternary climatic change and Phanerozoic or Late Tertiary weathering often are associated with coastal placer development. Regional process controls include present climate, sediment availability, waves, and winds. These studies reveal the diversity of tectonic settings, weathering histories, provenances, and processes of formation associated with coastal placers around the world. A regional-scale placer-development model derived from these case studies identifies controls acting at three scales: those acting over long geologic time periods, those acting over shorter geologic time periods, and those acting quasi-instantaneously. Similarly, spatial scalar divisions may meaningfully be constructed. Thus a hierarchical paradigm of spatial and temporal scale, in combination with regional studies and local morphogenetic investigations, assists in the development of regional exploration-model formulation.